Latching ferrite phase shifter having a predetermined phase shift when switched from one major remanent state to the other



April 25, 1967 L. R. WHICKER ET AL LATCHING FERRITE PHASE SHIFTER HAVING A rnniDETERMINED PHASE SHIFT WHEN SWITCHED FROM ONE MAJOR REMANENT STATE TO THE OTHER Filed Aug. 24, 1965 FIG-7.

3 Sheets-Sheet 2 THESHOLD g DETECTOR ELECTRONICALLY AND TRIGGER VARIABLE RESISTOR AMPLIFIER file 32 34 as 6 I4 33- 3a 33 30']:

A LATCH GARNET+FERRITE g 350 LU 3|5 LATCH GARNET :5: 300 3;, 250

g 225 LATCH GARNET v E |ao LATCH FERRITE E :50 I LATCH GARNET g5 I00 0 s. LATCH 1 GARNET Z 515 sis 5.'7 518 5'9 6T0 FREQUEN CY(GC) April 25, 1967 1.. R. WHICKER ET AL 3,316,506

LATCHING FERRITE PHASE SHIFTER HAVING A PREDETERMINED PHASE SHIFT WHEN SWITCHED FROM ONE MAJOR REMANENT STATE TO THE OTHER 3 Sheets-Sheet 3 Filed Aug. 24, 1965 GARNET FERRITE FREQUENCY(GC) FERRITE 5.6 5.7 FREQUENCWGC) lfi W O llll 1-- m 0 H 8 C T A L o o 6 o 3 6 Q IIIII. 4 O 2 F 0 0 o m w w Amwmmwmekmim mm Im .rzwmmmh=o R Q TEMPERATURE(C) United States Patent Ofiice 3,316,506 Patented Apr. 25, 1967 LATCHING FERRITE PHASE SHIFTER HAVING A PREDETED PHASE SHIFT WHEN SWITCHED FROM ONE MAJOR REMANENT STATE TO THE OTHER Lawrence R. Whicker, Severna Park, and Raymond R.

Jones, Baltimore, Md., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Aug. 24, 1965, Ser. No. 482,072 8 Claims. (Cl. 33324.1)

The present invention relates generally to microwave phase shifters, and more particularly relates to phase shifters for obtaining differential phase shift in n increments Where n is any positive integer.

The desirability of phase shifters for use in applications such as, for example, phased array antenna systems, is well established. Present latching ferrite phase shifters seek to provide a wide range of phase shift by utilizing several lengths of ferrite elements which are switched independently. Each ferrite element is separated by dielectric spacers. Separate power supplies are required for switching the individual elements. A wide variety of differential phase shifts are attainable by selectably switching these elements from one remanent state of magnetization to the other remanent state of magnetization. Still, the number of incremental phase shifts is limited to the combination of available switching ferrite elements.

An object of the present invention is to provide a microwave phase shifter which is simpler in design than previous shifters.

Another object of the present invention is to provide a microwave phase shifter capable of providing any number of differential phase shift increments.

Another object of the present invention is to provide a microwave phase shifter which is simpler in design and which has less insertion loss.

Another object of the present invention is to provide a microwave phase shifter wherein one driver only is required as compared to a driver for each element in a multi-bit shifter of the prior art.

The foregoing objects and other advantages are attained by providing in a microwave phase shifter 21 single ferrite element with an aperture longitudinally disposed therethrough. An electrical conductor extends through the aperture for connection to external circuitry which provides bidirectional current pulses. An important part of the present invention is the recognition that the hysteresis loop of magnetic materials when subjected to microwave frequencies is not completely rectangular or square and its slope remains nearly constant over considerable portions thereof. Hence, pulses of controlled amplitude directed along the electrical conductor extending through the element will set the flux to a state intermediate the remanent states of the major hysteresis loop characterizing the material or element. The element is reset by a pulse of opposite or other direction through the electrical conductor. An important feature of the present invention is the resetting of the magnetic flux within said ferrite element by a current pulse of sufficient magnitude to drive the element to a reference or first remanent state on its major hysteresis loop by driving the element into saturation where the major and minor hysteresis loops coincide.

Further objects and advantages of the present invention will be readily apparent from the following detailed description taken in conjunction with the drawing in which:

FIGURE 1 is an isometric drawing, partly in section, of an illustrative embodiment of the present invention;

FIG. 2 is a characteristic operating curve helpful in understanding the operation of the present invention;

FIG. 3 is a representative waveform utilized by the present invention;

FIG. 4 is a characteristic operating curve;

FIGS. 5 and 6 are electrical schematic diagrams of circuits which may be utilized by the present invention; and

FIGS. 7 through 10 are curves illustrating other operating characteristics of the present invention.

Referring to FIG. 1, a waveguide 2 having an entrance port 4 and an exit port 6, has longitudinally disposed therein a ferrite element 8 with a quarterwave matching transformer 10 at each end. An aperture 12 longitudinally extends through the ferrite element 8 and transforming members 10. An electrical conductor 14 extends through the aperture 12 and is brought out of the waveguide 2 at each of its ends through the transforming members 10.

The electrical conductor 14 is connected to a controlled amplitude pulsing circuit 16. The pulsing circuit 16 provides positive and negative or bidirectional current pulses. Referring to FIG. 2, a positive pulse exceeding a predetermined magnitude will magnetize the element 8 in a circumferential direction to saturation point, M Since the element is in the form of a toroid or closed ring, it will retain the larger part of its magnetization, the point of remanent magnetization M when the current pulse is removed. The element 8 is said to be latched at this point; namely +M The material of the element 8 is chosen to have a substantially square loop magnetization curve in which the remanent magnetization M is ahnost equal to the saturation magnetization M If a negative current pulse -1 is applied, the magnetization of the element will be reversed and the material will remain set at M when the current pulse is removed. Since the states of remanent magnetization M and M result from the saturation magnetization of the element 8 they are key points on a loop identified as the major hysteresis loop of the material making up the element 8. The cross section and length of the element 8 are chosen to shift microwave energy through the waveguide 2 a nominal 360 when the element 8 is switched from one latched or remanent state of magnetization M to the other state of remanent magnetization +M It is an important aspect of the present invention to note that the characteristic hysteresis loop is not completely square or rectangular with the slope of unity when the element 8 is subjected to microwave frequencies. Rather, the slope of the hysteresis loop is less than unity and nearly constant over considerable portions. Hence, the saturation state of the material can be selected by controlling the magnitude of current pulse from the circuit 16 to the conductor 14. Referring again to FIG. 2, assume the element 8 to be initially in a state of magnetic flux density corresponding to point M A controlled pulse of amplitude I through the electrical conductor will when removed establish a state of flux at point B along the minor hysteresis loop indicated by the arrows. Consequently, the microwave energy passing through the waveguide will react with the portion of magnetic moments which are properly aligned and an intermediate amount of phase shift will be obtained. If it is desired to obtain a different amount of differential phase shift, a large negative reset pulse of suflicient amplitude, I is pulsed to drive the element 8, upon removal of the pulse, to a state of remanent magnetization M Resetting of the core material assures repeat-ability and eliminates accumulative I errors after several switching operations.

A sample waveform of the pulsing sequence is as shown in FIG. 3. After reset current pulse, -I has been applied, a positive pulse, I, of suitable amplitude follows to pulse the magnetic material to any chosen intermediate state of magnetic flux density. For example, a pulse of controlled magnitude, I will result, when the pulse is removed, in the material assuming an intermediate state as indicated at point C along the minor hysteresis loop indicated by the arrows with a resultant greater shift in microwave energy through the waveguide.

FIG. 4 illustrates a characteristic curve D relating pulse amplitude to degrees of phase shift. A variation of differential phase shift of less than 1% has been obtained after cycling the element 8 several hundred times. The element 8 utilized to arrive at the curve D was of a garnet configuration. Of course, similar characteristic curves are easily plotted for gyromagnetic materials of other types.

One type of controlled amplitude pulsing circuit 16 is as illustrated in FIG. 5.v A capacitor 20 is charged to the magnitude of the V voltage supply through a switching device such as silicon controlled rectifier 21. Intermediate states of flux density are obtained by electronically adjusting the variable resistor 22 and threshold detector 23 to trigger a silicon controlled rectifier 24 when the desired'current level through the element 8 via the conductor 14 is reached. The large amplitude reset pulses, -1 are obtained by triggering a silicon controlled rectifier 25 to its on condition.

When a positive reset-negative controlled amplitude waveform is desired rather than the waveform of FIG. 3, then the circuit of FIG. 6 may be utilized. The large amplitude reset pulse is obtained by charging a capacitor 30 through the conductor 14 which extends through the element 8. The capacitor 30 is charged to a voltage V upon firing of an SCR 31. For intermediate states of magnetic flux density, the capacitor 30 is discharged through-any one or combination'networks'such as a single silicon controlled rectifier switch 32 and the series circuit combination of other SCRs 33 and resistors 34, 35 and 36 of varying magnitude. To permit discharge through any of the networks, the proper SCRs are trig- 'gered to the on, condition.

As can be seen from FIG. 4 an n increment phase shifter can be obtained by providing various amplitude positive pulses, I, along with accompanying negative reset pulses, I For example, eight controlled amplitude positive pulses are required to correspond to a present 3bit design phase shifter while 16 pulses are required for a 4 bit design.

' C-band model phase shifters have been fabricated.

, One such 'device employed a single element or ferrite material having a 41rM equal to 1700 gauss. Another utilized an element made from a temperature compensated garnet material having a 41rM equal to 1200 gauss. In each design, the length of the element 8 was adjusted to give a maximum of 360 differential :phase shift when latched ibetween remanent states on the major hysteresis 7 each device are illustrated in FIGS. 8 and 9. Slightly better'matching has been obtained in the ferrite design. It 15 seen that switching between either intermediate or remanent states does not effect the value of the SWR or the insertion loss.

Temperature dependence of the differential phase shift of the microwave energy has been noted for the garnet model by :switching between remanences and between remanents and an intermediate state as shown in FIG. 10. The intermediate state has a nearly flat phase shift characteristic over a temperature range from about 40 4 to degrees centigrade, while the 360 latch exhibits considerable variation.

It is to be noted that the temperature dependence of the differential phase shift was dependent upon which remanent state was used as a reference. That is, the temperature dependence obtained using negative resetpositive controlled amplitude pulses was different from that obtained when using positive reset-negative controlled amplitude pulses. Hence, the desirability of a1- ternate controlled amplitude pulsing circuit 16 as shown 7 in FIGS. 5 and'6 is apparent. Improved phase shift temperature characteristics when switching between remanence and most intermediate states may be obtained by compensating for the temperature variations by adjusting the pulse amplitudes, I, to the element 8. v

The single element current controlled latching ferrite phase shifter in accordance with the present invention offers several advantages over present phase shifters. The present invention is simple in structure, exhibits low insertion loss and can be used to obtain any desired number of steps of differential phase'shift. Moreover, for most applications, the amount of switching circuitry is reduced over presently available phase shifters.

While the present invention has been described with a degree of particularity for the purposes of illustration, it is to be understood that all modifications, alterations and substitutions within the spirit and scope of the present invention are herein meant to be included. For example, the use of elements, such as ferrites, having gyromagnetic properties for'the phase or attenuation of Wave energy is widely known and widely used in various applications, both in waveguide and transmission lines. Since it is the gyromagnetic properties of ferrites that are essential to the operation of this invention, the term ferrites has been used herein synonymously with gyromagnetic materials. Of course, other gyromagnetic materials may be utilized such as,.for example, spinel-type materials, garnet type ferrites, which contain rare earths. It is to be understood that in the appended claims herewith the term ferrite is meant to include any such material capable of providing phase shift for incident microwave energy when used in a suitable geometry and biased with a DC. magnetic field.

We claim as our invention;

1. In combination; a waveguide for the passage of energy; a single ferrite element longitudinally disposed Within said waveguide; said element having an aperture extending therethrough; an electrical conductor extending through said aperture; said element having a major positive remanent state of flux density and a major negative remanent state of flux density in response to a predetermined positive current pulse and a predetermined negative current pulse respectively on-said conductor; said element differentially phase shifting the energy through said wave-guide a nominal 360 when switched from one major remanent state to the other major remanent state; and controlled amplitude pulsing means connected to said conductor for resetting the flux to one of said major remanent states and for setting the flux to a selected state intermediate said remanent states whereby a selected lesser differential phase shift of said microwave energy occurs.

2. In combination; a waveguide for the passage of microwave energy; a single ferrite element longitudinally disposed within said waveguide; said element having an aperture extending therethrough; an electrical conductor extending through said aperture; said element having a major positive remanentstate and a major negative remanent state. of flux density in response to a predetermined positive current pulse and a predetermined negative current pulse respectively on said conductor; said microwave energy being shifted a predetermined number of degrees when said element is switched from one major remanent state to the other major remanent state; and controlled amplitude pulsing means connected to said conductor for setting the flux to a selected state intermediate said remanent state by first setting said element to one of said major remanent states and then setting said element to said selected intermediate state.

3. A differential phase shifter for microwave energy, the phase shift being in n increments where n is any positive integer, comprising, in combination; a wave-guide for the microwave energy; a single element of gyromagnetic material longitudinally disposed within said waveguide; said element characterized by having a hysteresis loop of slope less than unity and nearly constant over considerable portions thereof and a positive remanent state and a negative remanent state to shift the microwave energy through said waveguide a predetermined number of degrees when switched from one remanent state to the other remanent state; said element having an aperture extending longitudinally therethrough; an electrical conductor extending through said aperture; and means operatively connected to said electrical conductor for switching said element from one remanent state to another state including the other remanent state and intermediate states and returning said element to said one state after dilferentially shifting the microwave energy a number of degrees no larger than said predetermined number of degrees.

4. The apparatus of claim 3 wherein said predetermined number of degrees is a nominal 360 differential phase shift.

5. A multi-bit dilferential phase shifter comprising, in combination; a waveguide for the passage of microwave energy; a single ferrite element longitudinally disposed within said waveguide; said element characterized by having a major hysteresis loop including opposite states of remanent magnetization; said element chosen to provide a predetermined differential phase shift of the microwave energy through the waveguide when said element is switched from one said remanent state to the opposite remanent state; said element having an aperture extending longitudinally therethrough; an electrical conductor extending through said aperture; and means for providing a plurality of controlled amplitude pulses for selectively relaxing said element along a minor hysteresis loop from a remanent state to a state of magnetization between said opposite states for differentially shifting the phase of the microwave energy through the waveguide by an amount related to the size of the minor hysteresis loop.

6. The apparatus of claim 5 including means for resetting said element for the next controlled amplitude pulse by pulsing said electrical conductor with a current magnitude suflicient to reset said element to a remanent state on said major hysteresis loop.

7. The apparatus of claim 5 wherein said predetermined differential phase shift is 360.

8. The apparatus of claim 5 including a quarterwave matching transformer disposed at each end of said element; the aperture and electrical conductor extending through said transformers as well as said ferrite element.

No references cited.

HERMAN KARL SAALBACH, Primary Examiner.

P. GENSDER, Assistant Examiner. 

1. IN COMBINATION: A WAVEGUIDE FOR THE PASSAGE OF ENERGY; A SINGLE FERRITE ELEMENT LONGITUDINALLY DISPOSED WITHIN SAID WAVEGUIDE; SAID ELEMENT HAVING AN APERTURE EXTENDING THERETHROUGH; AN ELECTRICAL CONDUCTOR EXTENDING THROUGH SAID APERTURE; SAID ELEMENT HAVING A MAJOR POSITIVE REMANENT STATE OF FLUX DENSITY AND A MAJOR NEGATIVE REMANENT STATE OF FLUX DENSITY IN RESPONSE TOI A PREDETERMINED POSITIVE CURRENT PULSE AND A PREDETERMINED NEGATIVE CURRENT PULSE RESPECTIVELY ON SAID CONDUCTOR; SAID ELEMENT DIFFERENTIALLY PHASE SHIFTING THE ENERGY THROUGH SAID WAVE-GUIDE A NOMINAL 360* WHEN SWITCHED FROM ONE MAJOR REMANENT STATE TO THE OTHER MAJOR REMANENT STATE; AND CONTROLLED AMPLITUDE PULSING MEANS CONNECTED TO SAID CONDUCTOR FOR RESETTING THE FLUX TO ONE OF SAID MAJOR REMANENT STATES AND FOR SETTING THE FLUX TO A SELECTED STATE INTERMEDIATE SAID REMANENT STATES WHEREBY A SELECTED LESSER DIFFERENTIAL PHASE SHIFT OF SAID MICROWAVE ENERGY OCCURS. 